Daikin · Mini-split
U4 Transmission error between units
What this code means
Same family as Mitsubishi's E6 — a break in communication between the indoor and outdoor units.
Most likely causes
- Damaged or pinched interconnecting cable
- Corroded terminal connections
- Outdoor unit control board fault
What to try first
Inspect the interconnecting cable where it exits the wall for visible damage or chew marks.
Safety note: if this code returns after one clean reset, stop resetting it — repeated lockouts usually mean a real fault that needs a licensed technician. Never bypass a safety switch.
FAQ
What does Daikin error code U4 mean?
Transmission error between units. Same family as Mitsubishi's E6 — a break in communication between the indoor and outdoor units.
Can I fix Daikin code U4 myself?
Usually not. Inspect the interconnecting cable where it exits the wall for visible damage or chew marks. If the code returns after one reset, it needs a licensed technician.
What causes Daikin code U4?
The most common causes are: damaged or pinched interconnecting cable; corroded terminal connections; outdoor unit control board fault.
Other Daikin mini-split codes
All Daikin mini-split error codes →
Other mini-split brands: Mitsubishi · LG · Fujitsu · Gree · Carrier · Generic · Panasonic
This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.